xdg-desktop-menu: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/xdg-desktop-menu - from package: xdg-utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/xdg-desktop-menu - from package: xdg-utils

You may install the required package with command apt-get install {package}

Error in other languages:
xdg-desktop-menu: bevel nie gevind nie
xdg-desktop-menu: comandă negăsită
xdg-desktop-menu: comando não encontrado
xdg-desktop-menu: commande introuvable
xdg-desktop-menu: command not found
xdg-desktop-menu: käsku ei ole
xdg-desktop-menu: không tìm thấy lệnh
xdg-desktop-menu: komanda nerasta
xdg-desktop-menu: Kommando nicht gefunden.
xdg-desktop-menu: kommandot finns inte
xdg-desktop-menu: komut yok
xdg-desktop-menu: nie znaleziono polecenia
xdg-desktop-menu: níor aimsíodh an t-ordú
xdg-desktop-menu: no se encontró la orden
xdg-desktop-menu: no s'ha trobat l'ordre
xdg-desktop-menu: opdracht niet gevonden
xdg-desktop-menu: parancs nem található
xdg-desktop-menu: perintah tidak ditemukan
xdg-desktop-menu: príkaz nenájdený
xdg-desktop-menu: příkaz nenalezen
xdg-desktop-menu: команда не найдена
xdg-desktop-menu: командата не е открита
xdg-desktop-menu: 命令找不到
xdg-desktop-menu: コマンドが見つかりません